Wiist and Hand. 



99 



upper, or, hair stroke, in writing, since this movement is 

 effected by flexion of the first and extension of the second 

 and third phalanges, whereas the heavy, or, downstroke, is 

 the result of extension of the first phalanx by the extensor 

 communis digitorum, and of flexion of the second and third 

 phalanges by the powerful flexor sublimis and flexor pro- 

 fundus muscles. In addition to the above actions, the 

 palmar interossei adduct the index, ring and little fingers 

 towards the middle line, while the dorsal interossei abduct 

 the index, middle and ring fingers from the middle line ; 

 lastly, the palmaris brevis wrinkles up the integument of 

 the inner side of the palm of the hand. 



Movements of the Wrist Joint. The move- 

 ments permitted at the wrist joint proper, are flexion, ex- 

 tension, adduction and abduction, and their combination 

 circumduction. Not being a ball and socket joint, there 

 is no rotary movement permitted here, but this movement 

 of rotation is replaced by pronation and supination of the 

 radius. 



Extension at the wrist joint is freer than flexion, be- 

 cause the posterior portion of the articular surfaces of the 

 scaphoid, semilunar and cuneiform bones, is prolonged 

 farther downwards than the anterior portion ; while ad- 

 duction, i.e., movement towards the ulnar side, is freer 

 than abduction since the syloid process projects more on 

 the radial than on the ulnar side and impinging, therefore, 

 on the scaphoid, limits abduction. To supplement 

 the actions of the wrist joint proper, especially 

 flexion and extension, and to increase, therefore, 

 the usefulness of the hand, we have the midcarpal 

 and the carpo-metacarpal articulations. These ad- 

 mit of both flexion and extension, the former 

 movement being freer than the latter, while, in the case of 

 the mid-carpal joint, there is, in addition, a slight amount 



